This invention pertains to a food packing machine, and more particularly, to an improved food-cake-forming mechanism in such a machine. While, as those skilled in the art will recognize, the mechanism of the present invention is applicable to machines designed for the packing of various food products, such as various meat and vegetable products, the mechanism herein is described in conjunction with a machine for the packing of tuna fish, in so-called "chunk" or "flake" packs, in which application the mechanism has been found to have particular utility.
To explain the environment and operation of a conventional tuna packing machine, reference is made to prior U.S. Pat. No. 3,346,403 to Carruthers, entitled METHOD OF CONTROLLING THE FEED TO FOOD PACKING MACHINES, issued Oct. 10, 1967. By this reference, it is intended that the disclosure of such patent be incorporated herein to illustrate conventional packing-machine construction which may readily incorporate the improvement disclosed in the instant application.
In a machine like that disclosed in the prior patent, tuna in flake or chunk condition is fed into the machine, and thereby is directed into cylindrical cavities which are continuously moved through a path of travel. Pressure is applied to the product, subsequent to a cavity-filling operation, to fill voids, expel air, and to insure a substantially uniform homogeneous fill of tuna in the cavities. After appropriate pressure has been applied, the resulting cake of tuna is trimmed off to bring the amount which is to be canned (subsequently) to substantially a desired predetermined weight. Thereafter, the compressed tuna cake is transferred to a can or other container, and then subjected to the usual later canning processes.
One of the difficulties which has been encountered in the past in such a machine is control of compressed cake weight. Overfilling the ultimate consumer container with tuna results in a substantial loss to the canner. Underfilling presents problems such as the cost for inspection of underfilled cans, and the hand labor to bring the can up to weight by adding additional tuna.
Pressure to form a tuna cake in a cavity like that just mentioned is normally applied by a piston which is driven into the cavity containing a deposit of tuna chunks. Prior to action of the piston, naturally, tuna chunks are introduced into the cavity, and typically, are introduced in such a manner as to overfill the cavity with a mound extending over the cavity's top. Such a practice aids in assuring that there is an ample amount of tuna fish available for forming a desired-weight cake.
However, this practice introduces an important difficulty which is particularly addressed by the mechanism of the present invention. More specifically, and because of the mound of tuna which extends over a cavity's opening, experience over the years has shown that as a piston approaches the cavity's entrance while pressing down on the mound, tuna chunks in the mound tend to bridge the space between the piston and the cavity's entrance--in a manner requiring a larger-than-desired packing force to drive the piston into the cavity. The situation thus exists that, during a short span of movement of a piston into a cavity, such occurring just as the piston enters the cavity, a relatively high force is required to drive the piston properly into the cavity, but thereafter, this force must be reduced in order to avoid a too-great cake-forming force which could result, ultimately, in container overfilling. Thus, the problem has been how, successfully, to achieve a piston drive mechanism for cake-forming which takes care of the piston/cavity entry force problem, and which thereafter responds with a lowered and more appropriate cake-compressing force.
Where piston drive springs have been proposed and tried in the past, it has quickly been found that a spring having a sufficient force to overcome the bridging situation mentioned above, has too much force for the subsequent cake-compressing operation. Conversely, a spring sized to develop an appropriate cake-compressing force is typically too weak to overcome the bridging matter. Air-driven systems require elaborate regulation mechanism to solve the differential force problem.
A general object of the present invention is to provide a unique and relatively simple, but very effective, mechanism which takes into account the force considerations mentioned above, avoids the problems encountered in the past, and yields an extremely satisfactory cake-forming operation.
Yet another object of the invention is to provide such a mechanism which can easily be incorporated in a wide variety of conventional food-packing machine designs without requiring any significant adaptive modifications.
According to a preferred embodiment of the invention, as disclosed herein, the same is illustrated in the setting of a food packing (tuna) machine which employs, in a turret mechanism, a plurality of pistons for compressing and preparing cakes of tuna for canning. Each piston rides reciprocally in a carrier which is cam-driven toward and away from an associated cake-forming cavity, wherein the piston is intended, with its work face, to act against tuna chunks. Operation of the carrier and piston, as the latter moves initially into a cavity's entrance, is characterized by nonyieldable biasing, or driving, of the piston into the cavity. In essence, the piston and carrier, which are relatively reciprocable, bottom out against one another to define one limit position of movement of the piston relative to the carrier--with cam drive then imparted directly to the work face of the piston independent of any spring-biasing action. Immediately thereafter, that is, after the work face of the plunger has been driven into the cavity's entrance, a spring which is interposed between the carrier and piston, in a manner tending to extend the work face of the piston relative to the carrier, takes over piston drive functions, and promotes continued, but now yieldable, driving of the piston into the cavity. The strength of the selected spring is such that, under the circumstance now being described, with the piston inside the cavity, an appropriate preselected compression force is attained. Naturally, this force is a matter of design selection based upon the particular cake-forming needs--with selection being a matter merely of choosing an appropriate spring size.
The various objects and advantages which are attained by the invention will now become more fully apparent as the same is described in conjunction with the accompanying drawings.